What do those who believe 'have' when they 'have faith'? What traces does the experience of faith leave in the believer's existence? And can theologians assure that their studies will genuinely have something to do with 'the wholly Other'? Dietrich Bonhoeffer (1906-1945), operating within the framework of Karl Barth's (1886-1968) theology, addressed those questions in order to complete this framework. The ensuing dialogue between those great theologians affords us a deeper insight in fundamental concepts such as 'revelation', 'faith', 'christological concentration', 'analogy', 'church' and 'discipleship'. In this study, Edward van't Slot reads this dialogue with regard to both its historical and its theological significance. He shows what Bonhoeffer means when he attacks Barth's 'positivism of revelation', and compares it with Barth's earlier 'negativism of revelation'.